6.2: Lifetime of Single Panel LCOS Imagers

Yakovenko, S. Ye.; Konovalov, V. A.; Brennesholtz, Matthew S.

doi:10.1889/1.1811457

Cited by 10 publications

(9 citation statements)

References 2 publications

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“…For an LC material/alignment layer at a given wavelength, the degradation mechanism is not a linear function of the employed light intensity. 14 The higher intensity is more harmful than the low intensity even though their total UV dosage (intensity multiplied by exposure time) remains the same. To obtain a realistic result, in principle, we should measure the lifetime at several intensities, fit the data, and extrapolate back to the intensity of the actual LCD projector.…”

Section: Discussionmentioning

confidence: 99%

Photostability of liquid crystals and alignment layers

Wen

Gauza

2005

J. Soc. Inf. Display

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-Photostability of liquid-crystal (LC) materials and surface alignment layers was evaluated using a UV lamp and a blue laser beam. Both organic polyimide (PI) and inorganic silicon-dioxide (SiO 2 ) alignment layers were studied under nitrogen environment. Two commercial TFT-grade LC mixtures (low-birefringence MLC-9200-000 and high-birefringence TL-216) were used for comparisons. Results indicate that SiO 2 alignment layers are much more robust than PI layers, and low birefringence LCs are more stable than the high-birefringence ones. At the He-Cd laser wavelength (λ = 442 nm), both LC mixtures and SiO 2 alignment layers are hardly damaged. To lengthen the lifetime of an LCD projector, inorganic SiO 2 alignment layers, high-optical-density UV filter, long cutoff-wavelength blue filter, and short-conjugation (low birefringence) LC materials should be considered.Keywords -Liquid crystals, photostability, lifetime, alignment layers, inorganic SiO 2 , LCD projector. IntroductionPhotostability of liquid-crystal (LC) materials and alignment layers play a crucial role in affecting the lifetime of liquid-crystal-display (LCD) devices. [1][2][3][4] In direct-view displays, ultraviolet (UV) light is often used to seal the LC panels. In projection displays using liquid-crystal-on-silicon (LCOS), 5 the employed arc lamp is relatively bright. Although a cold mirror and a hot mirror are used to filter out the unwanted UV and infrared contents of the lamp, residual UV light could still penetrate into the LC panels and cause performance degradation. Even if the UV contents are completely filtered out, the blue wavelength might still be harmful to the LCD panels. These high-energy photons could cause gradual degradation of the organic alignment layers and the LC molecules. Once the LC medium is decomposed or the alignment layers deteriorated, the pretilt angle is changed and the consequent electro-optic effects are altered. 6 In this paper, we report the photostability of LC alignment layers and LC materials in the UV and blue wavelengths. Regarding the alignment layers stability, we studied the buffed polyimide (PI) and sputtered inorganic silicondioxide (SiO 2 ) alignment layers under nitrogen environment. On the LC-material stability studies, we selected two Merck LC mixtures: TL-216 (∆n = 0.20) and MLC-9200-000 (∆n = 0.08). A high birefringence LC mixture, such as TL-216, enables a thinner cell gap to be used. The advantages are twofold: (1) faster response time and (2) weaker fringing-field effect. For instance, the Philips color-sequential LCOS projector 7 uses a~1-µm cell gap in order to achieve fast response time and minimize the fringing-field effect. On the other hand, a low-birefringence LC mixture, such as MLC-9200-000, is commonly used for three-panel LCOS projectors. UV stability of LC alignment layersThe Hamamatsu UV light was delivered to the sample through a fiber bundle and collimated by a lens. The output light passed through a narrow-band interference filter centered at λ~365 nm. The light intensity ...

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Section: Discussionmentioning

confidence: 99%

Photostability of liquid crystals and alignment layers

Wen

Gauza

2005

J. Soc. Inf. Display

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“…Cells that showed uniform LC alignment and a pre-tilt between 3°and 5°were subjected to accelerated lifetime tests. 1 Accelerated lifetime tests showed that the lifetime of LCOS microdisplays with ion-milled DLC layers was a factor 0.5-0.7 shorter than the lifetime of LCOS microdisplays with conventional rubbed PI alignment layers. NEXAFS experiments (see next paragraph) showed that C = C bonds are broken during the ion-milling process.…”

Section: Lifetime Of Lcos Microdisplays With Ion-milled Dlc Alignmentmentioning

confidence: 98%

“…Experimental data have shown that Philips LMS imagers exceed the 20,000-hour lifetime requirement under 2.0 Mlux of illumination. 1 Due to future miniaturization of the LCOS microdisplay, the light load on the display will increase. High light fluxes will decompose several components of the microdisplay and will therefore reduce the lifetime of the panel.…”

Section: Introductionmentioning

confidence: 99%

Diamond‐like‐carbon LC‐alignment layers for application in LCOS microdisplays

Bol¹,

Dvorak²,

Arena³

2005

J Soc Info Display

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Abstract— To improve the lifetime and yield of LCOS microdisplays, non‐contact LC alignment techniques using inorganic materials are under investigation. This report focuses on oblique ion‐beam treatment of diamond‐like carbon (DLC) layers, and in particular on the influence of the ion dose on the LC alignment on DLC, keeping the ion‐beam angle (40°) and ion‐beam energy (170 eV) the same. LC alignment on ion‐milled DLC layers is uniform if the ion dose is between 3.8 × 10−4 C/cm2 and 5.5 × 10−3 C/cm2. Above and below this ion dose range, non‐uniform alignment is observed. NEXAFS experiments show that this is caused by lack of molecular anisotropy on the surface of the ion‐milled DLC layers. By varying the ion dose between 3.8 × 10−4 C/cm2 and 5.5 × 10−3 C/cm2, LC molecules have an average pre‐tilt between 3° and 5°, which is within the desired range for application in LCOS microdisplays. The lifetime of the LCOS microdisplays with ion‐milled DLC for projection‐TV application is, however, shorter than the lifetime of microdisplays with PI layers. Ion milling probably creates a reactive surface that is unstable under the high light fluxes used in projection TVs. A solution for this problem could be chemical passivation of the ion‐milled alignment layers. Initial experiments with passivation of ion‐milled PI resulted in an increase in lifetime, but the lifetime after passivation was still lower than the lifetime of rubbed PI layers (factor 0.7). Nevertheless, ion‐milling of DLC or PI can be a good alternative LC alignment technique in other LCD applications. LC‐alignment layers based on inorganic layers such as obliquely deposited SiO2 films would be a better option for application in LCOS microdisplays due to their higher light stability.

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“…XPS also revealed the important role of LC remnants (polymerized LC) in the loss of alignment and helped to understand better the mechanism of alignment degradation in LCOS cells. Further work 3,4 was dedicated to electro-optic studies. Wen 3 presented extensive experimental data about the degradation of electro-optic parameters and alignment of two LC mixtures.…”

Section: Introductionmentioning

confidence: 99%

“…In Ref. 4, the primary focus was the methods of panel lifetime testing and the lifetime dependency on the light intensity and UV-cutoff wavelength.…”

Section: Introductionmentioning

confidence: 99%

A lifetime model for LCOS panels under intense illumination

Konovalov¹,

Fauchille²,

Yakovenko³

2006

J. Soc. Inf. Display

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Abstract— The mechanisms of photochemical reactions occurring during the operation of LCOS panels under intense illumination are analyzed. Regardless of the liquid‐crystal‐mixture formulation, light may generate radicals in the liquid crystal and the polyimide alignment layer. The interaction of these radicals modifies the PI surface and causes alignment degradation. Using kinetic equations for these processes, a lifetime model for the LCOS panels is developed. This new model of lifetime dependence versus light intensity is found to be in agreement with experimental data. This model verifies the TN LCOS panel lifetime to be in excess of 50,000 hours for RPTV applications.

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6.2: Lifetime of Single Panel LCOS Imagers

Cited by 10 publications

References 2 publications

Photostability of liquid crystals and alignment layers

Photostability of liquid crystals and alignment layers

Diamond‐like‐carbon LC‐alignment layers for application in LCOS microdisplays

A lifetime model for LCOS panels under intense illumination

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